Electronic component packaging relates to an electrical and/or mechanical package that houses one or more elements that comprise an electronic component. Electronic component packaging plays an important role in the performance and reliability of a computer system. The package serves a number of purposes, including electrical path provisioning for signals and power distribution, thermal paths for heat extraction and cooling, and mechanical protection against undesired internally and externally generated forces.
Conventional electronic component packaging include transistor packages, e.g., small outline transistor (“SOT”), and integrated circuit packages, e.g., small outline integrated circuit (“SOIC”), thin small outline package (“TSOP”), shrink small outline package (“SSOP”), thin shrink small outline package (“TSSOP”), plastic leaded chip carrier (“PLCC”), quarter-size small outline package (“QSOP”), very small outline package (“VSOP”), low profile quad flat pack (“LQFP”), plastic quad flat pack (“PQFP”), ceramic quad flat pack (“CQFP”), thin quad flat pack (“TQFP”), pin grid array (“PGA”), and ball grid array (“BGA”).
It is sometimes desirable to stack a number of components as part of the package. For example, Sun Microsystems' high-end server microprocessor module package is comprised of a number of electrical and mechanical components that are mated together electrically and/or mechanically. With reference to FIG. 1, the high-end server microprocessor module package 100 is comprised of one or more screws 105, one or more springs 110, a heat sink 115, one or more bushings 120, a thermal interface 125, a microprocessor package 140 comprised of one or more semiconductor die 130 mounted on a ceramic substrate 135, a socket 145, a printed circuit board 150, an electrical insulating interface 155, and a bolstering plate 160. The interface between 140 and 150 is often referred to as the L2 interface. To ensure the functionality and reliability of the module package, it is necessary to precisely control the surface shape of each component in the stack.
The overall shape of the module package is determined by the interplay of relative stresses between the components that comprise the stack. The relative stresses at each interface depend on the intrinsic properties of the material and are typically temperature dependent. For example, one component might have a coefficient of thermal expansion that is different from that of another component to which it is mated. As a result, the surface shape will change when two or more components with different coefficients of thermal expansion are mated and thermal expansion or contraction takes place. Thus, it is critical to characterize the surface shape of the components before they are assembled into the module package as well as to characterize the surface shape of the resulting module package.
EQ. 1 represents the commonly used surface shape parameter that is utilized in industry to describe the surface shape of a package.Warpage=zmax−zmin  (1)The warpage parameter, also known as co-planarity or flatness, is defined as the difference between the maximum and minimum surface elevation (z-coordinate) of the package when placed on a horizontal seating plane (z=0).
The Joint Electron Device Engineering Council (“JEDEC”) has promulgated a number of standards that relate to the measurement of coplanarity using the warpage parameter, such as JEDEC Standard No. 22-B108A entitled “Coplanarity Test for Surface-Mount Semiconductor Devices” and JEDEC Standard No. 22-B112 entitled “High Temperature Package Warpage Measurement Methodology.” Conventional metrology utilizing the warpage parameter typically assumes that the surface shape is spherically symmetric. Any deviation from that assumption is typically treated as tolerance or margin in the warpage.
FIG. 2 shows a topographic or contour map of the surface shape of a package with spherical symmetry. The x-axis 210 and y-axis 220 represent the dimensions of the electronic component in the direction of the x-axis 210 and the y-axis 220 measured in units of millimeters. The z-axis is represented by a color coded scale 230 that represents the elevation of the electronic component from the horizontal seating plane in units of micrometers (μm). With respect to FIG. 2, the centermost countour 240 represents a 50 μm elevation from the horizontal seating plane.
However, there are a number of more complex surface shapes encountered in practice. FIG. 3 shows a topographic or contour map of the surface shape of a package with axial symmetry of the cylindrical type. The x-axis 310 and y-axis 320 represent the dimensions of the electronic component in the direction of the x-axis 310 and y-axis 320 measured in units of millimeters. The z-axis is represented by a color coded scale 330 that represents the elevation of the electronic component from the horizontal seating plane in units of micrometers. With respect to FIG. 3, the centermost countour 340 represents a 50 μm elevation from the horizontal seating plane. Note that, in contrast to the spherically symmetric surface shape shown in FIG. 2, the 50 μm elevation shown in FIG. 3 is a region that extends the entire length of the y-axis 320 centered with respect to the x-axis 310.
FIG. 4 shows a topographic or contour map of the surface shape of a package with axial symmetry of the saddle type. The x-axis 410 and y-axis 420 represent the dimensions of the electronic component in the direction of the x-axis 410 and y-axis 420 measured in units of millimeters. The z-axis is represented by a color coded scale 430 that represents the elevation of the electronic component from the horizontal seating plane in units of micrometers. With respect to FIG. 4, the surface shape exhibits what is referred to as saddle symmetry. The upper portion 440 and lower portion 450 of the saddle represent a 50 μm elevation from the horizontal seating plane.
As shown above, FIG. 2, FIG. 3, and FIG. 4 represent the surface shape of a package with spherical symmetry, axial symmetry of the cylindrical type, and axial symmetry of the saddle type respectively. Note that each of FIG. 2, FIG. 3, and FIG. 4 exhibit symmetry with respect to the x-axis 210, 310, 410 and the y-axis 220, 320, 420. However, surface shapes are often twisted due to the interplay between surfaces that are mated electrically and/or mechanically or inadvertent non-uniform stress induced as part of the fabrication process of a component.
FIG. 5 shows a topographic or contour map of the surface shape of a package with twisted spherical symmetry. The x-axis 510 and y-axis 520 represent the dimensions of the electronic component in the direction of the x-axis 510 and the y-axis 520 measured in units of millimeters. The z-axis is represented by a color coded scale 530 that represents the elevation of the electronic component from the horizontal seating plane in units of micrometers. With respect to FIG. 5, the surface shape, that originally had spherical symmetry, is twisted, meaning that the elevation from the horizontal seating plane is twisted in the direction of the lower left corner of the electronic component package. Thus, the lower left corner 540 represents a 50 μm elevation from the horizontal seating plane.
FIG. 6 shows a topographic or contour map of the surface shape of a package with twisted axial symmetry of the cylindrical type. The x-axis 610 and y-axis 620 represent the dimensions of an electronic component in the direction of the x-axis 610 and the y-axis 620 measured in units of millimeters. The z-axis is represented by a color coded scale 630 that represents the elevation of the electronic component from the horizontal seating plane in units of micrometers. With respect to FIG. 6, the surface shape, that originally had axial symmetry of the cylindrical type, is twisted, meaning that the elevation from the horizontal seating plane is twisted in the direction of the lower left corner of the electronic component package. Thus, the lower left corner 640 represents a 50 μm elevation from the horizontal seating plane.
FIG. 7 shows a topographic or contour map of the surface shape of a package with twisted axial symmetry of the saddle type. The x-axis 710 and y-axis 720 represent the dimensions of the electronic component in the direction of the x-axis 710 and y-axis 720 measured in units of millimeters. The z-axis is represented by a color coded scale 730 that represents the elevation of the electronic component from the horizontal seating plane in units of micrometers. With respect to FIG. 7, the surface shape exhibits saddle symmetry twisted in the direction of the lower left corner of the electronic component package. Thus, the lower portion 740 of the saddle represents a 50 μm elevation from the horizontal seating plane.
One of ordinary skill in the art will recognize that there are a number of other surface shapes realized in practice that deviate from spherical symmetry.